U.S. patent application number 14/318017 was filed with the patent office on 2014-10-16 for glass substrate and method for producing glass substrate.
This patent application is currently assigned to Asahi Glass Company, Limited. The applicant listed for this patent is Asahi Glass Company, Limited. Invention is credited to Hideaki HAYASHI, Kuniaki HIROMATSU, Yuki KONDO, Yo NAKAHARA, Jun SASAI.
Application Number | 20140305502 14/318017 |
Document ID | / |
Family ID | 48697257 |
Filed Date | 2014-10-16 |
United States Patent
Application |
20140305502 |
Kind Code |
A1 |
SASAI; Jun ; et al. |
October 16, 2014 |
GLASS SUBSTRATE AND METHOD FOR PRODUCING GLASS SUBSTRATE
Abstract
A method for producing a glass substrate includes (a) a step of
forming molten glass having a temperature T2 less than or equal to
1500.degree. C. on molten tin having an iron concentration greater
than or equal to 100 ppm to produce a glass ribbon having a
temperature T4 less than or equal to 1100.degree. C. and a
logarithm log .rho. greater than or equal to 8.8, and (b) a step of
cooling the glass ribbon to room temperature to produce the glass
substrate. The temperature T2 represents a temperature when a
logarithm of a viscosity .eta. (dPas) is 2, the temperature T4
represents a temperature when the logarithm of the viscosity .eta.
(dPas) is 4, and the logarithm log .rho. represents a logarithm of
a volume resistivity .rho. (.OMEGA.cm) at 150.degree. C.
Inventors: |
SASAI; Jun; (Tokyo, JP)
; KONDO; Yuki; (Tokyo, JP) ; NAKAHARA; Yo;
(Tokyo, JP) ; HIROMATSU; Kuniaki; (Tokyo, JP)
; HAYASHI; Hideaki; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Asahi Glass Company, Limited |
Tokyo |
|
JP |
|
|
Assignee: |
Asahi Glass Company,
Limited
Tokyo
JP
|
Family ID: |
48697257 |
Appl. No.: |
14/318017 |
Filed: |
June 27, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2012/083117 |
Dec 20, 2012 |
|
|
|
14318017 |
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Current U.S.
Class: |
136/256 ; 501/11;
65/99.2 |
Current CPC
Class: |
C03C 3/087 20130101;
H01L 31/022466 20130101; Y02P 70/50 20151101; C03B 18/02 20130101;
H01L 31/03923 20130101; Y02P 70/521 20151101; H01L 31/03925
20130101; Y02E 10/541 20130101; H01L 31/0392 20130101; C03B 18/18
20130101; C03C 4/0085 20130101 |
Class at
Publication: |
136/256 ;
65/99.2; 501/11 |
International
Class: |
C03B 18/18 20060101
C03B018/18; C03C 4/00 20060101 C03C004/00; H01L 31/0224 20060101
H01L031/0224 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 2011 |
JP |
2011-286738 |
Claims
1. A glass substrate that is formed on molten tin having an iron
concentration that is higher than an equilibrium concentration for
achieving equilibrium with a glass to be produced, the glass
substrate comprising a glass material having: a logarithm log .rho.
greater than or equal to 8.8, where the logarithm log .rho.
represents a logarithm of a volume resistivity .rho. (.OMEGA.cm) at
150.degree. C.; a temperature T4 less than or equal to 1100.degree.
C., where the temperature T4 represents a temperature when a
logarithm of a viscosity .eta. (dPas) is 4; and a temperature T2
less than or equal to 1500.degree. C., where the temperature T2
represents a temperature when the logarithm of the viscosity .eta.
(dPas) is 2.
2. The glass substrate according to claim 1, further comprising at
least one material selected from a group including K.sub.2O, BaO,
and SrO at a concentration exceeding an unavoidable impurity
concentration.
3. The glass substrate according to claim 2, wherein a total
concentration of K.sub.2O+BaO+SrO expressed as an oxide-based mass
ratio is greater than or equal to 1 mass %.
4. The glass substrate according to claim 1, wherein the iron
concentration of the molten tin is greater than or equal to 100
ppm.
5. The glass substrate according to claim 1, further comprising a
transparent conductive oxide layer.
6. A method for producing a glass substrate comprising: (a) a step
of forming molten glass having a temperature T2 less than or equal
to 1500.degree. C. on molten tin having an iron concentration
greater than or equal to 100 ppm to produce a glass ribbon having a
temperature T4 less than or equal to 1100.degree. C. and a
logarithm log .rho. greater than or equal to 8.8, where the
temperature T2 represents a temperature when a logarithm of a
viscosity .eta. (dPas) is 2, the temperature T4 represents a
temperature when the logarithm of the viscosity .eta. (dPas) is 4,
and the logarithm log .rho. represents a logarithm of a volume
resistivity .rho. (Q cm) at 150.degree. C.; and (b) a step of
cooling the glass ribbon to room temperature to produce the glass
substrate.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application is a continuation application filed
under 35 U.S.C. 111(a) claiming benefit under 35 U.S.C. 120 and
365(c) of PCT International Application No. PCT/JP2012/083117 filed
on Dec. 20, 2012 and designating the U.S., which claims priority to
Japanese Patent Application No. 2011-286738 filed on Dec. 27, 2011.
The entire contents of the foregoing applications are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a glass substrate and a
method for producing a glass substrate.
[0004] 2. Description of the Related Art
[0005] The so-called "high transmittance glass substrates" having
high transmittance are used as glass substrates for solar
batteries, for example.
[0006] Glass substrates may be produced in an industrial setting
using the so-called float process. The float process involves
producing a glass substrate by introducing molten glass into a
float bath, which accommodates molten tin under a reducing
atmosphere, forming a glass ribbon on the molten tin surface, and
cooling the glass ribbon to room temperature. In this case, tin
ions intrude upon the surface of the glass ribbon that comes into
contact with the molten tin (referred to as "bottom face"
hereinafter) through thermal diffusion such that strong reducing
conditions are created at the outermost surface. Also, in a case
where the iron concentration within glass and the iron
concentration within tin are not in a state of equilibrium, iron
diffusion occurs in the direction toward equilibrium. As a result,
in a case where the iron concentration within the molten tin is
lower than the tin concentration within the glass ribbon, the iron
concentration within the molten tin increases until reaching
equilibrium. On the other hand, in a case where the iron
concentration within the molten tin is higher than the tin
concentration within the glass ribbon, the iron concentration
within the glass ribbon decreases until reaching equilibrium.
[0007] In the case of producing the "high transmittance glass
substrate" using the float process, attention needs to be directed
to the intrusion of iron components from the molten tin side to the
glass ribbon side at the bottom face. This is because iron
components exhibit light absorbing properties when residing within
glass under an ion state. For example, divalent iron ions have an
absorption peak at a wavelength around 1000 nm. Trivalent iron ions
have an absorption peak at a wavelength around 380 nm. In addition,
under strong reducing conditions, iron ions are known to exhibit
strong coloration (amber coloration) having a peak at 450 nm.
Accordingly, when such iron ions are contained in the glass ribbon,
transmittance of the resulting glass substrate may be degraded.
Notably, when a high concentration of iron components intrude upon
the glass ribbon, it may become difficult to produce the "high
transmittance glass substrate" itself.
[0008] In light of the above, Japanese Patent No. 4251552 (referred
to as "Patent Document 1" hereinafter) discloses forming a "high
transmittance glass substrate" using low-iron molten tin having an
iron concentration that is greater than or equal to 55 ppm and less
than 100 ppm.
[0009] According to the method disclosed in Patent Document 1, a
"high transmittance glass substrate" is produced by using molten
tin having a low iron concentration to prevent intrusion of iron
from the molten tin side to the glass ribbon side.
[0010] However, the above method may not be considered a practical
solution owing to the following reasons.
[0011] Generally, multiple types of glass substrates are produced
using the same float process equipment. For example, a glass
substrate for a glass member of a vehicle (characterized by having
a relatively high iron concentration) and a high transmittance
glass substrate are often produced using the same float process
equipment. Because a glass substrate for a glass member of a
vehicle often has a relatively high iron concentration, the amount
of iron contained within molten tin after producing the glass
substrate for the glass member of a vehicle may exceed 100 ppm, for
example.
[0012] Thus, in the case of implementing the method disclosed in
Patent Document 1, after producing the glass substrate for the
glass member of a vehicle, the molten tin within the float bath has
to be replaced with molten tin having a lower iron concentration in
the case of producing a high transmittance glass substrate using
the same equipment, for example. Replacing molten tin in this
manner may lead to a decrease in the equipment operation rate and
an increase in costs, for example.
[0013] Thus, there is still a demand for a technique for producing
a high transmittance glass substrate while preventing the intrusion
of iron components from the molten tin side to the glass ribbon
side.
[0014] In light of the above, it is an object of the present
invention to provide a glass substrate production technique for
effectively preventing the intrusion of iron components even when
molten tin having a relatively high iron concentration is used in a
float process.
SUMMARY OF THE INVENTION
[0015] According to one embodiment of the present invention, there
is provided a glass substrate that is formed on molten tin having
an iron concentration that is higher than an equilibrium
concentration for achieving equilibrium with a glass to be
produced. The glass substrate comprising glass material having a
logarithm log .rho. greater than or equal to 8.8, where the
logarithm log .rho. represents a logarithm of a volume resistivity
.rho. (.OMEGA.cm) at 150.degree. C.; a temperature T4 less than or
equal to 1100.degree. C., where the temperature T4 represents a
temperature when a logarithm of a viscosity .eta. (dPas) is 4; and
a temperature T2 less than or equal to 1500.degree. C., where the
temperature T2 represents a temperature when the logarithm of the
viscosity .eta. (dPas) is 2.
[0016] According to another embodiment of the present invention, a
method for producing a glass substrate is provided that includes:
(a) a step of forming molten glass having a temperature T2 less
than or equal to 1500.degree. C. on molten tin having an iron
concentration greater than or equal to 100 ppm to produce a glass
ribbon having a temperature T4 less than or equal to 1100.degree.
C. and a logarithm log .rho. greater than or equal to 8.8, where
the temperature T2 represents a temperature when a logarithm of a
viscosity .eta. (dPas) is 2, the temperature T4 represents a
temperature when the logarithm of the viscosity .eta. (dPas) is 4,
and the logarithm log .rho. represents a logarithm of a volume
resistivity .rho. (.OMEGA.cm) at 150.degree. C.; and (b) a step of
cooling the glass ribbon to room temperature to produce the glass
substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a flowchart illustrating an exemplary flow of a
method for producing a glass substrate according to an embodiment
of the present invention; and
[0018] FIG. 2 illustrates an exemplary configuration of a solar
battery including the glass substrate according to the
embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] In the following, a mode for carrying out the present
invention will be described with reference to the drawings. Note,
however, that the present invention is not limited to the
embodiments described below but may include numerous variations and
modifications that may be made without departing from the scope of
the present invention.
[0020] A glass substrate according to one embodiment of the present
invention may be a glass substrate having high transmittance that
may be used as a substrate for a solar battery, for example.
[0021] A method for producing a glass substrate according to an
embodiment of the present invention is characterized by
including:
[0022] (a) a step of forming molten glass having a temperature T2
less than or equal to 1500.degree. C. on molten tin having an iron
concentration greater than or equal to 100 ppm to produce a glass
ribbon having a temperature T4 less than or equal to 1100.degree.
C. and a logarithm log .rho. greater than or equal to 8.8, where
the temperature T2 represents a temperature when the logarithm of
the viscosity .eta. (dPas) of the molten glass is 2 (simply
referred to as "T2" hereinafter), the temperature T4 represents a
temperature when the logarithm of the viscosity .eta. (dPas) of the
glass ribbon is 4 (simply referred to as "T4" hereinafter), and the
logarithm log .rho. represents the logarithm of the volume
resistivity .rho. (.OMEGA.cm) of the glass ribbon at 150.degree.
C.; and
[0023] (b) a step of cooling the glass ribbon to room temperature
to produce a glass substrate.
[0024] As described above, in the known method, the iron
concentration within the molten tin is controlled to be greater
than or equal to 55 ppm and less than 100 ppm to prevent the
intrusion of iron from the molten tin side to the glass ribbon side
in producing a high transmittance glass substrate.
[0025] However, such a method has limited applicability to
currently adopted general industrial methods for producing glass
substrates. For example, in a case where a glass substrate for a
glass member of a vehicle (characterized by having a relatively
high iron concentration) and a high transmittance glass substrate
are produced using the same equipment, the amount of iron contained
within molten tin may often exceed 100 ppm, for example. If the
molten tin within the float bath is to be replaced with molten tin
having a lower iron concentration each time a high transmittance
glass substrate is to be produced, the equipment operation rate may
be decreased and costs may be increased, for example.
[0026] In this respect, the present embodiment is characterized by
having the molten glass prepared such that log .rho. of the glass
ribbon may be greater than or equal to 8.8. Also, the present
embodiment is characterized by having the molten glass prepared
such that T4 may be less than or equal to 1100.degree. C.
[0027] Note that in the present embodiment, the volume resistivity
.rho. represents a value measured in accordance with the ASTM
C657-78 method.
[0028] Also, in the present embodiment, T4 represents a value
measured by a rotational viscometer. Normally, the logarithm of the
viscosity .eta. (dPas) of glass is equal to 4 when the glass
transitions from a molten state to a molding process in a tin bath.
Thus, T4 corresponds to the temperature of the glass ribbon when it
comes into contact with the molten tin.
[0029] Inventors of the present invention have found that when log
.rho. of the glass ribbon is greater than or equal to 8.8, movement
of various types of ions from the molten tin side to the glass
ribbon side may be effectively prevented and high diffusion
prevention characteristics can be achieved. Accordingly, in the
present embodiment, intrusion of iron components and tin components
from the molten tin side to the glass ribbon side may be
effectively prevented even when the glass ribbon comes into contact
with molten tin. That is, in the present embodiment, intrusion of
iron components from the molten tin side to the glass ribbon side
may be effectively prevented even when the concentration of iron
contained in the molten tin is greater than or equal to 100
ppm.
[0030] Also, in the present embodiment, T4 is arranged to be less
than or equal to 1100.degree. C. That is, the temperature of the
glass ribbon when it comes into contact with the molten tin is
controlled to be less than or equal to 1100.degree. C. Thus,
reactivity between the glass ribbon and the molten tin may be
controlled, and intrusion of iron components from the molten tin
side to the glass ribbon side may be further prevented.
[0031] Further, the present embodiment is characterized in that T2
of the molten glass is arranged to be less than or equal to
1500.degree. C.
[0032] Note that T2 represents a value measured by a rotational
viscometer.
[0033] Generally, an equilibrium reaction between divalent iron
(ions) and trivalent iron (ions) may be expressed by the following
formula (1).
Fe.sub.2O.sub.3=2FeO+1/2O.sub.2 (1)
[0034] This equilibrium tends to shift to the right side as the
temperature increases.
[0035] In this case, visible light transmittance Tv is known to
decrease as the amount of iron components (total amount of divalent
iron ions and trivalent iron ions) contained within a glass
substrate increases. Also, solar radiation transmittance Te is
known to decrease as the amount of divalent iron ions contained in
the glass substrate increases. Accordingly, in order to produce a
"high transmittance glass substrate" having both high visible light
transmittance Tv and high solar radiation transmittance Te, the
amount of divalent iron ions contained within the glass substrate
needs to be controlled in addition to controlling the total amount
of iron components contained within the glass substrate.
[0036] As described above, in the present embodiment, the molten
glass is prepared such that log .rho. of the glass ribbon may be
greater than or equal to 8.8 and T4 may be less than or equal to
1100.degree. C.
[0037] Also, in the present embodiment, T2 of the molten glass is
less than or equal to 1500.degree. C. Accordingly, in the present
embodiment, progression of the reaction of formula (1) in the right
side direction may be controlled, and even when a slight amount of
iron components are contained within the glass substrate, the
amount of divalent iron ions affecting the solar radiation
transmittance Te may be controlled.
[0038] Thus, in the present embodiment, a "high transmittance glass
substrate" having both high visible light transmittance Tv and high
solar radiation transmittance Te may be produced.
[0039] As can be appreciated, in the present embodiment, a high
transmittance glass substrate having high transmittance may be
produced using a general float process equipment without having to
pay attention to the concentration of iron contained in the molten
tin.
[0040] Also, in the method for producing a glass substrate
according to the present embodiment, glass having a volume
resistivity .rho. such that log .rho. is greater than or equal to
8.8 is produced, and T4 of the molten glass is arranged to be less
than or equal to 1100.degree. C.
[0041] In this case, in addition to preventing the intrusion of
iron components contained in the molten tin, the molten tin itself
may be effectively prevented from intruding into the glass ribbon
side.
[0042] For example, one undesired phenomenon resulting from
performing a thermal process on the glass substrate includes the
development of haze on the surface of the glass substrate referred
to as "bloom". Such a phenomenon occurs when excessive tin ions are
diffused on the bottom face of the glass substrate such that a
tin-rich layer is formed. That is, because the tin-rich layer and
the glass substrate bulk side have different thermal expansion
coefficients, when the glass substrate including the tin-rich layer
is thermally processed, haze may appear on the tin-rich layer as a
result of the mismatch in thermal expansion behaviors.
[0043] In the method according to the present embodiment, glass
having a volume resistivity .rho. such that log .rho. is greater
than or equal to 8.8 is produced. Also, T4 of the molten gas is
arranged to be less than or equal to 1100.degree. C. Accordingly,
tin may be effectively prevented from intruding into the glass
ribbon side from the surface of the glass ribbon that comes into
contact with the molten tin. Thus, the method according to the
present embodiment has an additional advantageous effect of
preventing the so-called bloom phenomenon.
[0044] (Method for Producing Glass Substrate of Present
Embodiment)
[0045] In the following, the method for producing a glass substrate
according to the present embodiment is described in greater
detail.
[0046] FIG. 1 schematically illustrates an exemplary flow of the
method for producing a glass substrate according to the present
embodiment.
[0047] As illustrated in FIG. 1, the method for producing a glass
substrate according to the present embodiment includes:
[0048] (a) a step of forming molten glass having a temperature T2
less than or equal to 1500.degree. C. on molten tin having an iron
concentration greater than or equal to 100 ppm to produce a glass
ribbon having a temperature T4 less than or equal to 1100.degree.
C. and a logarithm log .rho. greater than or equal to 8.8, where
the temperature T2 represents a temperature when the logarithm of
the viscosity .eta. (dPas) of the molten glass is 2, the
temperature T4 represents a temperature when the logarithm of the
viscosity .eta. (dPas) of the glass ribbon is 4, and the logarithm
log .rho. represents the logarithm of the volume resistivity .rho.
(.OMEGA.cm) of the glass ribbon at 150.degree. C. (step S110);
and
[0049] (b) a step of cooling the glass ribbon to room temperature
to produce a glass substrate (step S120).
[0050] The above steps are described in detail below.
[0051] (Step S110)
[0052] First, a glass raw material to be used as the material for
molten gas is prepared.
[0053] The glass raw material includes a glass base composition raw
material, a cullet, and a refining agent. The refining agent may
be, for example, SO.sub.3, SnO.sub.2, and/or Sb.sub.2O.sub.3.
[0054] The glass raw material is prepared such that T2 of the
molten glass may be less than or equal to 1500.degree. C. Also, the
glass raw material is prepared such that T4 of the glass ribbon may
be less than or equal to 1100.degree. C. and log .rho. of the glass
ribbon may be greater than or equal to 8.8.
[0055] Note that although the method of preparing such glass raw
material is not particularly limited, as one example, the glass raw
material may be prepared in the manner described below.
[0056] For example, materials such as K.sub.2O, BaO, and/or SrO may
be added to the glass base composition raw material, and the amount
at which the materials are added may be controlled to produce a
glass substrate having the above-described characteristics. In one
specific example, K.sub.2O, BaO, and/or SrO may be added to the
glass base composition raw material such that the concentration of
K.sub.2O, BaO, and/or SrO within the glass substrate exceeds the
concentration at which the K.sub.2O, BaO, and/or SrO may exist as
unavoidable impurities. By adding appropriate amounts of K.sub.2O,
BaO, and/or SrO, log .rho. of the glass may be increased, the glass
in the molten glass state and the glass ribbon state may be
maintained at a relatively low viscosity, and T2 and T4 may be
decreased.
[0057] The K.sub.2O, BaO, and/or SrO (total concentration of
K.sub.2O+BaO+SrO) may be included at an oxide-based mass ratio of
at least 1 mass %, and more preferably at least 1.5 mass %, with
respect to the glass raw material. By arranging the concentration
to be in the above range, the glass raw material may be stably
adjusted such that log .rho. may be greater than or equal to
8.8.
[0058] Also, the K.sub.2O, BaO, and/or SrO (total concentration of
K.sub.2O+BaO+SrO) may be included at an oxide-based mass ratio of
no more than 7 mass %, and more preferably no more than 5 mass %,
with respect to the glass raw material. By arranging the
concentration to be in the above range, T2 may be maintained within
the desired temperature range, for example.
[0059] Note that the "oxide-based mass ratio" refers to the
composition of various components contained in glass expressed as
an oxide mass ratio, assuming all oxides and combined salts used in
the glass raw material of the present embodiment are decomposed and
turned into oxides upon being melted.
[0060] Next, the glass raw material prepared in the above manner is
melted to form molten glass. The melting temperature depends on the
glass raw material. For example, in the case where soda-lime-silica
glass is used, the melting temperature may be approximately
1300.degree. C. to approximately 1600.degree. C.
[0061] Next, the molten glass is introduced into a float bath
chamber that is under a controlled atmosphere. Normally, the
atmosphere of the float bath chamber is controlled to a reducing
atmosphere including hydrogen. A bath filled with molten tin
(molten tin bath) is arranged in the float bath chamber. In the
present embodiment, the iron concentration of the molten tin may be
greater than or equal to 100 ppm; that is, the iron concentration
may exceed 100 ppm such as 150 ppm or greater.
[0062] The molten glass introduced into the float bath chamber is
formed into a glass ribbon on the molten tin surface.
[0063] In the present embodiment, the glass ribbon is formed such
that log .rho. may be greater than or equal to 8.8. In this way,
iron components may be effectively prevented from intruding into
the glass ribbon side from the surface of the glass ribbon that
comes into contact with the molten tin.
[0064] Also, in the present embodiment, T4 is arranged to be less
than or equal to 1100.degree. C. That is, the temperature of the
glass ribbon upon coming into contact with the molten tin is
controlled to be less than or equal to 1100.degree. C. In this way,
reaction between the glass ribbon and the molten tin may be
suppressed, and intrusion of iron components and tin components
from the molten tin side may be further prevented.
[0065] Further, in the present embodiment, molten glass having the
temperature T2 less than or equal to 1500.degree. C. is used. In
this way, even in a case where iron components intrude into the
glass ribbon, the amount of divalent iron ions within the glass
ribbon may be effectively controlled.
[0066] As can be appreciated from the above, inventors of the
present invention have found that iron components and tin
components can be effectively prevented from intruding and
diffusing into the glass ribbon side by adjusting the properties of
the glass raw material such that log .rho. of the glass ribbon may
be greater than or equal to 8.8, T4 may be less than or equal to
1100.degree. C., and T2 may be less than or equal to 1500.degree.
C.
[0067] (Step S120)
[0068] Next, the glass ribbon formed in step S110 is discharged
from the float bath chamber and is cooled to room temperature. In
this way, the glass substrate of the present embodiment may be
produced.
[0069] In the method for producing a glass substrate according to
the present embodiment, iron components may be effectively
prevented from intruding into the glass substrate, and the amount
of divalent iron ions within the glass substrate may be effectively
controlled. Accordingly, the glass substrate obtained by
implementing the method of the present embodiment may have high
transmittance.
[0070] (Glass Substrate of Present Embodiment)
[0071] The glass substrate of the present embodiment may be
produced in the manner described above, for example. Note, however,
that the glass substrate of the present embodiment may also be
produced through other methods.
[0072] The glass substrate of the present embodiment is
characterized by:
[0073] being formed on molten tin having an iron concentration that
is greater than an equilibrium concentration for achieving
equilibrium with the glass to be produced (e.g. molten tin having
an iron concentration greater than or equal to 100 ppm);
[0074] having log .rho. greater than or equal to 8.8;
[0075] having T2 less than or equal to 1500.degree. C.; and
[0076] having T4 less than or equal to 1100.degree. C.
[0077] In the glass substrate of the present embodiment, the
concentration of iron components may be effectively controlled.
Accordingly, in the glass substrate of the present embodiment,
absorption at the wavelength of 1000 nm caused by divalent iron
ions may be effectively prevented. Also, absorption at the
wavelength of 450 nm caused by amber coloration may be effectively
prevented. In this way, the glass substrate of the present
embodiment may have high transmittance.
[0078] In the glass substrate of the present embodiment, log .rho.
of the glass substrate may be arranged to be within a range greater
than or equal to 8.8 and less than or equal to 12.0.
[0079] Also, in the glass substrate of the present embodiment, T2
may be arranged to be within a range greater than or equal to
1350.degree. C. and less than or equal to 1500.degree. C.
[0080] Further, in the glass substrate of the present embodiment,
T4 may be arranged to be within a range greater than or equal to
900.degree. C. and less than or equal to 1100.degree. C.
[0081] Note that the composition of the glass substrate of the
present embodiment is not particularly limited as long as the glass
substrate is adjusted to have the above-described characteristics.
As one example, the glass substrate of the present embodiment may
have a composition as indicated in the following Table 1, which
represents the oxide mass ratios of various components.
TABLE-US-00001 TABLE 1 COMPOSITION mass % SiO.sub.2 68~75
Al.sub.2O.sub.3 0~2.5 CaO 0~15 MgO 0~12 Na.sub.2O 5~20 K.sub.2O
0.8~5 SrO 0~1 BaO 0~1 K.sub.2O + SrO + BaO 1.1~7 Fe.sub.2O.sub.3
(TOTAL IRON) 0~0.06
[0082] As further examples, the glass substrate of the present
embodiment may have a composition as represented in Table 2 or
Table 3 below.
TABLE-US-00002 TABLE 2 COMPOSITION mass % SiO.sub.2 69~74
Al.sub.2O.sub.3 0.3~2.3 CaO 3~12 MgO 1~10 Na.sub.2O 7~17 K.sub.2O
1.0~4.5 SrO 0.1~0.8 BaO 0.1~0.8 K.sub.2O + SrO + BaO 1.5~6
Fe.sub.2O.sub.3 (TOTAL IRON) 0~0.05
TABLE-US-00003 TABLE 3 COMPOSITION mass % SiO.sub.2 69.3~73
Al.sub.2O.sub.3 0.5~2.1 CaO 5~10 MgO 3~8 Na.sub.2O 9~15 K.sub.2O
1.3~4.0 SrO 0.2~0.7 BaO 0.2~0.7 K.sub.2O + SrO + BaO 2~5
Fe.sub.2O.sub.3 (TOTAL IRON) 0~0.03
[0083] Note that in the three types of compositions described
above, at least a part of K.sub.2O may be replaced by BaO and/or
SrO, for example.
[0084] By arranging the composition of the glass substrate to have
the composition ranges indicated in Tables 1-3, glass characterized
by having T2 less than or equal to 1500.degree. C. and T4 less than
or equal to 1100.degree. C. may be stably produced.
[0085] (Application of Glass Substrate of Present Embodiment)
[0086] In the following, an exemplary application of the glass
substrate according to the present embodiment is described.
[0087] The glass substrate of the present embodiment may be used as
a substrate of a solar battery, for example. In the following, a
solar battery including the glass substrate of the present
embodiment is described with reference to FIG. 2.
[0088] FIG. 2 is a cross-sectional view illustrating an exemplary
configuration of a solar battery 200 including the glass substrate
of the present embodiment.
[0089] As illustrated in FIG. 2, the solar battery 200 includes a
glass substrate 210 having a first surface 212 and a second surface
214, and a solar battery element 230 arranged on the first surface
212 of the glass substrate 210. Note that although not illustrated
in FIG. 2, the solar battery 200 may further include an
anti-reflection coating (not shown) arranged on the second surface
214 of the glass substrate 210.
[0090] The solar battery element 230 includes a transparent
conductive layer (first electrode layer) 250, a photoelectric
conversion layer (power generating layer) 260, and a back surface
conductive layer (second electrode layer) 270 arranged in this
order from the glass substrate 210 side.
[0091] The transparent conductive layer 250 may be formed by a
layer having SnO.sub.2 as a main component, a layer having ZnO as a
main component, or a layer made of tin-doped indium oxide (ITO),
for example. Of the above layers, a layer having SnO.sub.2 as a
main component may be particularly suitable in view of material
costs, mass production capability, and the potential to minimize an
impact on the photoelectric conversion layer (power generating
layer) 260 when components of the transparent conductive layer 250
intrude into the photoelectric conversion layer (power generating
layer) 260. Note that "main component" refers to a component
contained at an oxide mass ratio of at least 90 mass %.
[0092] Examples of the layer having SnO.sub.2 as a main component
include a layer made of SnO.sub.2, a layer made of fluorine doped
tin oxide (FTO), and antimony doped tin oxide (ATO), for
example.
[0093] The transparent conductive layer 250 may be formed by
thermal decomposition, CVD (chemical vapor deposition), sputtering,
vapor deposition, ion plating, and spraying, for example.
[0094] The thickness of the transparent conductive layer 250 is
normally within a range of 200 nm to 1200 nm.
[0095] The photoelectric conversion layer (power generating layer)
260 is normally made of a semiconductor thin film. Examples of
semiconductor thin films that may be used include an amorphous
silicon based semiconductor thin film, a microcrystalline silicon
based semiconductor thin film, a compound semiconductor (e.g. CdTe
based semiconductor) thin film, and an organic semiconductor thin
film. Also, two or more of the above semiconductor thin films may
be layered to form the photoelectric conversion layer (power
generating layer) 260.
[0096] The thickness of the photoelectric conversion layer (power
generating layer) 260 may be 50 nm to 500 nm in the case where an
amorphous silicon based semiconductor is used, 500 nm to 5000 nm in
the case where a microcrystalline silicon based semiconductor is
used, 500 nm to 6000 nm in the case where layers of an amorphous
silicon based semiconductor and a microcrystalline semiconductor
are used, 500 nm to 10 .mu.m in the case where a CdTe (cadmium
telluride) based semiconductor is used.
[0097] The back surface conductive layer 270 may be made of a
material having no optical transparency, a material having optical
transparency, or layers of the above materials. Examples of a
material having no optical transparency include silver and
aluminum. Examples of a material having optical transparency
include ITO, SnO.sub.2, and ZnO. In the case of using a an
optically transparent material as the back surface conductive layer
270, an anti-reflection layer may be arranged on the surface of the
back surface conductive layer 270 opposite the photoelectric
conversion layer 260, for example. Note that materials such as
silver, aluminum, an alloy thereof, or white ink may be used as the
anti-reflection layer, for example.
[0098] The thickness of the back surface conductive layer 270 is
normally in the range of 100 nm to 10 .mu.m.
[0099] In the present example, the glass substrate of the present
embodiment is used as the glass substrate 210 of the solar battery
200.
[0100] As described above, in the glass substrate 210 of the
present embodiment, the concentration of iron components may be
effectively controlled so that the glass substrate may have high
transmittance. That is, in the glass substrate 210, absorption of
light particularly in the wavelength range of approximately 1000 nm
may be effectively prevented. In this way, the solar battery 200
including the glass substrate 210 of the present embodiment may
achieve improved efficiency, for example.
[0101] Note that a solar battery using the glass substrate of the
present embodiment is not limited to the solar battery 200 as
described above. For example, the glass substrate of the present
embodiment may also be used in a CIGS (copper indium gallium
selenide) based compound solar battery, a crystalline silicon based
solar battery, and a glass encapsulated thin film solar battery
cover glass.
WORKING EXAMPLES
[0102] In the following, working examples of the present embodiment
are described.
Working Example 1
[0103] In the present example, two types of glass substrates (glass
substrates A and B) with different values for log .rho. were
produced by implementing the float process using a tin bath having
an iron concentration of approximately 150 ppm. Further, the
transmittance of the glass substrates A and B were evaluated.
[0104] (Glass Substrate Production)
[0105] The glass substrates A and B were arranged to have the
composition of the soda-lime-silica glass as represented by the
above Table 1. The target thicknesses of the glass substrates A and
B were both arranged to be 3.9 mm.
[0106] Note that the volume resistivity .rho. of the glass
substrates A and B were measured in accordance with the ASTM
C657-78 method as described below.
[0107] First, the glass substrate subject to evaluation was cut
into a sample having dimensions of approximately 50 mm in height
and approximately 50 mm in width. Further, both faces of the sample
were optically polished to obtain a thickness of approximately 3.5
mm.
[0108] Next, metal aluminum films were formed on both sides of the
sample using the vapor deposition method. The metal aluminum films
were used as electrodes to measure the volume resistivity of the
sample under three different temperature conditions of 100.degree.
C., 150.degree. C., and 300.degree. C.
[0109] The measurement results obtained by measuring the volume
resistivity of the sample at the above measurement temperatures
were plotted against the reciprocals of the measurement
temperatures. Based on the slope A and intercept B of the resulting
line, the logarithm of the volume resistivity .rho. (.OMEGA.cm) was
calculated using the following formula (2).
log .rho.=A/T+B (2)
[0110] The following Table 4 indicates the glass composition, T4,
T2, and the logarithm log .rho. of the glass substrates A and
B.
TABLE-US-00004 TABLE 4 LOGARITHM OF VOLUME TRANSMITTANCE
RESISTIVITY WAVE- WAVE- GLASS GLASS COMPOSITION (wt %) .rho.
(.OMEGA.cm) T4 T2 LENGTH LENGTH SUBSTRATE SiO.sub.2 Al.sub.2O.sub.3
CaO MgO Na.sub.2O K.sub.2O Fe.sub.2O.sub.3 log .rho. (.degree. C.)
(.degree. C.) 450 nm 1000 nm A 71.06 1.91 7.70 5.19 12.35 1.53
0.008 8.92 1045 1466 91.05 90.08 B 71.32 1.89 7.49 5.04 13.91 0.05
0.008 8.23 1034 1455 90.80 89.80
[0111] (Glass Substrate Transmittance Evaluation)
[0112] Next, the above two types of glass substrates A and B were
used to measure their transmittance at the wavelength 450 nm and
the wavelength 1000 nm. Generally, amber coloration has an
absorption peak at a wavelength of around 450 nm. Also, divalent
iron ions have an absorption peak at a wavelength of around 1000
nm. The above two absorption coefficients are comparatively greater
than the absorption coefficient of trivalent iron ions, which has
an absorption peak at around a wavelength of 380 nm. Thus, by
evaluating the transmittance at the above two wavelengths 450 nm
and 1000 nm, an overall transparency of the glass substrate may be
determined to some extent.
[0113] Note that the transmittance was measured by preparing
samples of the glass substrates A and B by arranging the glass
substrates into 40.times.40 mm plates and measuring the samples
using a spectrophotometer (LAMBDA 950 by PerkinElmer Inc.).
[0114] The results of the measurement are indicated in the
"Transmittance" column of the above Table 4.
[0115] As can be appreciated from these measurement results, the
glass substrate A exhibiting a value of log .rho. greater than 8.8
has a higher transmittance compared to the transmittance of the
glass substrate B exhibiting a value of log .rho. less than
8.8.
[0116] According to the present example, a glass substrate with a
value of log .rho. greater than or equal to 8.8 may be obtained by
controlling the concentration of K.sub.2O within the glass
substrate. Also, the values of T2 and T4 may be maintained within
their respective desired ranges. Further, the glass substrate
having the above characteristics can achieve high transmittance at
both of the wavelengths 450 nm and 1000 nm.
[0117] That is, by arranging log .rho. of the glass substrate to be
greater than or equal to 8.8, arranging T4 to be less than or equal
to 1100.degree. C., and arranging T2 to be less than or equal to
1500.degree. C., intrusion of iron components into the glass ribbon
may be prevented during production of the glass substrate, and in
this way, the glass substrate may achieve high transmittance at the
wavelengths 450 nm and 1000 nm.
Working Example 2
[0118] In the present example, a measurement sample was created by
depositing a transparent conductive layer on one surface of a glass
substrate, and the transmittance of the measurement sample at the
wavelength 1000 nm was evaluated.
[0119] Note that the glass substrates A and B used in the above
Working Example 1 were used to create the measurement sample in the
present example. That is, measurement samples were obtained by
depositing a tin oxide layer on one surface of each of the glass
substrates A and B by implementing a general CVD process. In the
following descriptions, the measurement sample including the glass
substrate A is referred to as "measurement sample A", and the
measurement sample including the glass substrate B is referred to
as "measurement sample B". The thickness of the tin oxide layer was
arranged to be approximately 500 nm. Note that the method for
measuring the transmittance used in the present example was the
same as that used in the above Working Example 1.
[0120] The measurement results obtained by measuring the
transmittance in the present example indicated that for the
measurement sample A, the transmittance at wavelength 1000 nm was
83.7%. On the other hand, for the measurement sample B, the
transmittance at wavelength 1000 nm was 83.3%.
[0121] As can be appreciated from the above measurement results,
even in the case where the glass substrates A and B are arranged
into measurement samples by depositing conductive layers thereon, a
higher transmittance may still be achieved by the measurement
sample A compared to the measurement sample B.
Working Example 3
[0122] In the present example, the measurement samples A and B
prepared in the above Working Example 2 were used to conduct a DHB
(Dump Heat Bias) test.
[0123] In the DHB test, electrical and thermal durability of the
transparent conductive layer can be evaluated at the same time.
[0124] The DHB test was conducted in the following manner.
[0125] First, the measurement sample A (or measurement sample B)
was heated to a temperature within a range of 50.degree. C. to
200.degree. C. Note that although DHB test procedures implemented
on the measurement sample A are described below, the same
procedures were implemented on the measurement sample B.
[0126] Next, while maintaining the measurement sample A in the
heated state, an external power supply was used to apply a voltage
of 500 V to the measurement sample A. The voltage was applied to
the measurement sample A for 15 minutes in a manner such that the
glass substrate side of the measurement sample A constitutes the
positive (anode) side and the transparent conductive layer side
constitutes the negative (cathode) side.
[0127] Next, after stopping the heating and voltage application,
the measurement sample A was arranged inside a constant-temperature
bath where the temperature and humidity are controlled, and an
exposure test was conducted on the measurement sample A. The
humidity within the constant-temperature bath was controlled to a
relative humidity of 100%, and the temperature within the
constant-temperature bath was controlled to be 50.degree. C. The
exposure was conducted for one hour.
[0128] After the exposure test, appearance observations were made
on the measurement sample A to evaluate whether exfoliation of the
transparent conductive layer has occurred. Note that in this
evaluation, the occurrence of exfoliation at the corresponding
temperature was determined when exfoliation could be visually
recognized from at least one portion of the measurement sample
A.
[0129] The test results indicated that for the measurement sample
A, no exfoliation occurred after the exposure test when the heating
temperature upon voltage application was less than or equal to
150.degree. C. On the other hand, the test results indicated that
for the measurement sample B, exfoliation of the transparent
conductive layer occurred when the heating temperature upon voltage
application exceeded 120.degree. C.
[0130] As can be appreciated from the above test results, stronger
adhesion between the glass substrate and the transparent conductive
layer may be achieved by the measurement sample A compared to the
measurement sample B.
[0131] Also, based on the above test results, the adhesion between
the glass substrate and the transparent conductive layer may
presumably be maintained under harsher conditions by using the
glass substrate of the present embodiment as opposed to the
conventional glass substrate.
[0132] According to one aspect of the present embodiment, a method
for producing a glass substrate may be provided that can
effectively prevent the intrusion of iron even in a case where
molten tin having a relatively high iron concentration is used in a
float process. According to another aspect of the present
embodiment, a glass substrate may be provided that is produced
using molten tin having a relatively high iron concentration in a
manner such that intrusion of iron may be effectively
prevented.
[0133] The present embodiment may be applied to a high
transmittance glass substrate that is required to have high
transmittance such as a glass substrate of a solar battery.
[0134] Although the present invention has been described above with
respect to certain illustrative embodiments and examples, the
present invention is not limited to these embodiments and examples
but includes numerous variations and modifications that may be made
within the scope of the present invention.
* * * * *